1. Field of Invention
Distributed Bragg reflector (DBR) systems and methods that may be used with micro-electromechanical (MEMS) devices.
2. Description of Related Art
In xerographic color printing applications, it is desirable to have systems that measure the color accuracy of the printing. For example, spectrophotometers may be used with color printers to perform color sensing and measurement. Spectrophotometers may also be used for color sensing and measurement in xerography.
A spectrophotometer having a Fabry-Perot cavity filter may be integrated with a silicon photodetector, and then an optical fiber may be used for inputting light vertically to sense the color. The Fabry-Perot cavity thickness may be tuned electrostatically to resolve the spectral distribution of the transmitted light signal. A charge drive mode may be used to tune the Fabry-Perot cavity filter to avoid electrostatic instability that results from using a voltage drive mode. This configuration provides better linearity than the voltage drive mode.
Distributed Bragg reflectors (DBR) are widely used for enhancing the performance of optoelectronic devices such as light emitting devices, spectrophotometers, modulators and photodetectors. For example, a DBR may be used to increase the reflectivity, e.g., resolution, of a MEMS based full width array Fabry-Perot spectrophotometer that can be used for in-line xerographic color measurement. For some DBR applications, the number of DBR layers is limited due to economical considerations such as fabrication costs.
When forming DBRs, the thickness of each layer of the DBR must be determined. A high reflectance that is uniform over the optical band of the DBR is desired. In order to obtain the uniform high reflectance over the optical band, the thickness of each layer of the DBR may determined by using λ0/4n, where λ0 is the center wavelength of the optical band and n is the optical refraction index of the layer material. While using this method may enhance the reflectance of the DBR near λ0, the reflectance away from λ0, e.g., a wavelength that is adjacent to the center wavelength may not be enhanced to a desired level.